In UMTS (Universal Mobile Telecommunications System) networks, for the purpose of higher data rates, low delay and the like, Long Term Evolution (LTE) has been specified (Non-Patent Literature 1).
In LTE, as multiple access schemes, a scheme based on OFDMA (Orthogonal Frequency Division Multiple Access) is used on downlink, and a scheme based on SC-FDMA (Single Carrier Frequency Division Multiple Access) is used on uplink.
Further, for the purpose of wider bands and higher speed than LTE, for example, a successor system called LTE Advanced or LTE Enhancement (also called LTE-A) to LTE has been studied and specified as LTE Rel-10/11. A system band in Rel-10/11 includes at least one component carrier (CC) with a system band of the LTE system as one unit. It refers to carrier aggregation (CA) thus aggregating a plurality of CCs to widen the band.
In LTE Rel-12 that is a further successor system to LTE, various scenarios are studied where a plurality of cells is used in different frequency bands (carriers). In the case where radio base stations for forming a plurality of cells are substantially the same, it is possible to apply the above-mentioned CA. On the other hand, when radio base stations for forming respective cells are completely different from one another, it is studied applying dual connectivity (DC).